This invention relates to sample alignment for a scanning electron microscope and, more particularly, to apparatus for obtaining the appropriate sample alignment prior to placement of the sample in the scanning electron microscope.
During the manufacture of certain integrated circuit chips, a machine known as a photoresist stepper is utilized to define photoresist lines on the integrated circuit chip wafer. To insure that the stepper is working properly, the widths of the photoresist lines are measured to determine if they meet specifications. In order to do this, the stepper is caused to create an array of parallel lines on a wafer, the wafer is cleaved at a 90.degree. angle to the lines to provide a cross sectional examination sample, and the sample is examined using a scanning electron microscope. To obtain proper measurements, the sample must be held in the scanning electron microscope so that the electron beam is precisely aligned parallel to the photoresist lines. If there is a misalignment, two problems are encountered. First, one edge of the image of each line will be very bright (edge blooming), making it impossible to accurately determine the positions of edges and therefore the widths of the lines. The second problem is that the apparent widths of the lines will be somewhat reduced due to being viewed at an angle. If these measurements are altered by even a small percent, the resulting product can be detrimentally affected. It would therefore be desirable to be able to accurately align a sample for examination in a scanning electron microscope.
In the past, such alignment was effected after the sample was placed in the scanning electron microscope. Present high resolution scanning electron microscopes are not capable of providing easy and accurate alignment of the sample in all angular directions. It would therefore be desirable to have apparatus and a procedure for aligning such a sample prior to its placement in the scanning electron microscope.